1. Field of the Invention
This invention pertains to the field of treatment of human papillomavirus disease using photodynamic therapy. More specifically, it relates to the use of a topical hematoporphyrin composition that can be absorbed into diseased tissue thus enabling application of phototherapy to localized skin and mucosal growths.
2. Description of the Prior Art
Photochemotherapy is a rapidly developing method for treatment of malignant diseases in humans and animals. Photodynamic therapy (PDT) involves destruction of tissue that retains a photosensitivizing agent by exposing the tissue to light of the appropriate wavelength, most commonly in the red area between 625 and 635 nm. The agent hematoporphyrin derivative (HPD), or its active component dihematoporphyrin ether (DHE), has been found to selectively localize in abnormal tissue such as malignancies or papillomas. As such, HPD or DHE (hereinafter referred to as HPD/DHE) can be injected intravenously and allowed to migrate to tumorous sites. Subsequent exposure of the site to light of the appropriate wavelength causes destruction of the tumor, most likely by a process involving production of excited metastable molecular oxygen and toxic oxygen radicals, which lead to disruption of the cell membranes by lipid oxidation and protein sulfhydryl oxidation.
Although photodynamic therapy has been used successfully for the treatment of metastatic breast tumors, endometrial carcinomas, bladder tumors, malignant melanoma, Kaposi's sarcoma, basal cell carcinoma, chondrosarcoma, squamous cell carcinoma, prostate carcinoma, laryngeal papillomas, mycosis fungoides, superficial cancer of the tracheobronchial tree, and cutaneous/mucosal papilloma, it still has its drawbacks. The most predominant drawback is the fact that systemic injection of a photosensitizing agent requires the patient to avoid bright light, especially sunlight, for periods of 4 to 6 weeks. Consequently, the use of HPD/DHE has been limited to patients with severe disease.
As an alternative to intravenous injection of photoreactive agents, various researchers have attempted to directly inject HPD/DHE into tumors. Amano, et al., Journal of Urology 139, 392 (1988) have reported that high porphyrin levels in HPD injected tissue, and low porphyrin levels in surrounding tissues, indicate that such a method may be a viable alternative in cases where there are single lesions that are directly accessible.
Papilloma diseases, however, are often associated with multiple skin/mucosal growths which are frequently inaccessible to injection. Therefore a composition that could be applied topically, possibly even by the patients themselves prior to receiving the appropriate light treatment, would significantly enhance the usefulness of HPD/DHE therapy. McCullough, et al. Journal of Investigative Dermatology 81, 528 (1983) have reported the development of a topical lyophilized hematoporphyrin derivative formulation for the treatment of psoriasis and other cutaneous diseases. Using HPD in conjunction with azone and N-methylpyrrolidone, they demonstrated that exposure of a treated area of guinea pig skin to red light resulted in significant erythema and inhibition of epidermal DNA synthesis.
Although such topical hematoporphyrin formulations are useful in the treatment of cutaneous and subcutaneous diseases, HPD/DHE has not been found to be generally useful for the treatment of papillomavirus disease because of its inability to penetrate the tissue sufficiently to allow complete destruction of the growths. Utilization of HPD or DHE in aqueous solution on papillomavirus induced warts is not effective because the solutions are incapable of penetrating the lesions. Rather, they merely dry on the surface. Combinations of lyophilized HPD or DHE with commercially available carrying agents for topical application also fail, due either to loss of activity as a result of lyophilization of the HPD/DHE, or because the HPD/DHE is only partially soluble and the particulate portion does not penetrate the papilloma or normal skin. As a result, although photodynamic therapy using intravenous HPD derivative has proven useful for treatment of laryngeal papillomas, cutaneous experimental and naturally occurring lesions, and other forms of tumors, currently available therapies such as removal by use of CO.sub.2 laser or surgical excision are more commonly used with accessible growths.
The above problems associated with the prior art use of photodynamic treatment are overcome in the present invention by the development of a topical hematoporphyrin derivative formulation that can be applied directly to tumorous sites. The active compounds of the HPD/DHE are transported into the growth, which, upon exposure to red light with a wavelength of 625 to 635 nm, is destroyed.